Water-absorbent resin and method for producing the same

Abstract

The present invention relates to a water-absorbing resin and a method for manufacturing the same. The method for manufacturing the same is to perform a polymerization reaction on an acid group-containing monomer using a specific amount of a foaming agent under pressure sealing to obtain a core layer having a specific surface porosity, and then perform a surface cross-linking reaction on the core layer using an acyclic monoterpene alcohol having a carbon number of 10 to 12 and a surface cross-linking agent, so that the water-absorbing resin obtained has both good water-absorbing properties and superior deodorizing efficacy.

Description

Technical Field

[0001] This invention relates to a water-absorbing resin and a method for manufacturing the same, and more particularly to a water-absorbing resin prepared using a foaming agent and an acyclic monoterpene alcohol and a method for manufacturing the same. Background Technology

[0002] Absorbent polymers are widely used in agriculture and horticulture as water-retaining agents, in building materials as anti-dew condensation agents, in materials for removing moisture from petroleum, as waterproof coatings for cable outer layers, and in hygiene products. Examples include diapers, feminine hygiene products, and disposable wipes, with diapers being the most common.

[0003] Currently, the main development direction is functional diapers, especially adult diapers. In addition to improving absorbency and dryness, research is also focused on deodorizing effects. Based on the demand for deodorizing capabilities, various studies are actively underway to develop absorbent resins with deodorizing abilities while maintaining the original absorbent properties.

[0004] In the technical field to which this invention pertains, existing methods for manufacturing deodorizing absorbent resins involve adding zeolite particles during the polymerization reaction to disperse the zeolite particles within the absorbent resin, thereby imparting deodorizing capabilities, as disclosed in US Patent Publication No. 5,980,879. However, the amount of zeolite added is at least 25%, significantly reducing the absorbency of the absorbent resin. Furthermore, US Patent Publication No. 201,502,90052 discloses adding activated carbon or zeolite particles to the absorbent core of diapers. Similarly, while this provides deodorizing capabilities, the aforementioned particles can leak into production equipment or even remain suspended in the factory air, potentially harming the health of personnel on-site.

[0005] Patent Publication No. WO2009048145 discloses a method for preparing a water-absorbing resin, in which bamboo extract or tea extract is added to the surface of the water-absorbing resin or during the polymerization reaction. Because the extract affects the polymerization reaction, it reduces the absorption capacity of the water-absorbing resin and also increases the residual monomer content, causing skin redness and swelling. Furthermore, in US Patent Publications Nos. 20030004479 and 20040048955, powdered bamboo or tea is added to the surface of the water-absorbing resin. Because these powders have low dispersibility and are difficult to mix evenly with the water-absorbing resin, their deodorizing ability is reduced.

[0006] Furthermore, in US Patent Publication No. 6,663,949, European Patent Publication No. EP1,404,385, and US Patent Publication No. 7,868,075, activated carbon, nano-silver ions, or zeolite coated with silver ions are used to reduce odor. European Patent Publication No. EP1,275,404 discloses mixing cyclodextrin or its derivatives with absorbent resin to reduce odor. Additionally, US Patent Publication No. 20,150,306,272 describes heat-treating absorbent resin with 1,2-decanediol to reduce odor. However, these patents do not effectively improve the deodorizing efficacy of absorbent resin and only offer slightly better suppression of ammonia.

[0007] On the other hand, Patent Publication No. WO2003 / 028778 discloses a method for preparing a water-absorbing resin, wherein an antibacterial water-absorbing resin is prepared by lowering the pH value of the water-absorbing resin to achieve a deodorizing effect. In US Patent Publication No. 20010053807, the addition of glycine can also reduce odor. However, the water-absorbing resin prepared by this method has a poor absorption rate under pressure.

[0008] Japanese Patent Publication No. 1995165981 discloses a mixture of absorbent resin and a phosphate compound, and Japanese Patent Publication No. 1999116829 discloses a mixture of absorbent resin and a silicate compound. While the aforementioned mixtures can enhance the antibacterial ability of the absorbent resin to achieve a deodorizing effect, they also reduce the absorbency of the absorbent resin under pressure.

[0009] In view of this, there is an urgent need to develop a new method for manufacturing water-absorbing resins in order to overcome the above-mentioned shortcomings of existing methods for manufacturing water-absorbing resins. Summary of the Invention

[0010] In view of the above-mentioned problems, one aspect of the present invention is to provide a method for manufacturing a water-absorbing resin. This manufacturing method utilizes a specific amount of foaming agent and a specific acyclic monoterpene alcohol to enable the water-absorbing resin to possess both good water absorption properties and superior deodorizing effects.

[0011] Another aspect of the present invention is to provide a water-absorbing resin. This water-absorbing resin is prepared using the aforementioned method for manufacturing water-absorbing resins.

[0012] According to one aspect of the present invention, a method for manufacturing a water-absorbing resin is provided. In this method, an acid-containing monomer, an initiator, a foaming agent, and an internal crosslinking agent are provided, and the acid-containing monomer is polymerized in a pressure-sealed apparatus to obtain a core layer, wherein the amount of the acid-containing monomer used is 100 parts by weight, and the amount of the foaming agent used is greater than 0 parts by weight and not more than 3.14 parts by weight. Then, a surface crosslinking agent and an auxiliary agent are provided, and the core layer is subjected to a surface crosslinking reaction to form a shell layer, wherein the shell layer covers the outer surface of the core layer, and the auxiliary agent comprises an acyclic monoterpene alcohol having 10 to 12 carbon atoms.

[0013] According to one embodiment of the present invention, the foaming agent comprises an alkali metal carbonate and / or an alkaline earth metal carbonate.

[0014] According to another embodiment of the present invention, the amount of the acid-containing monomer used is 100 parts by weight, and the amount of the foaming agent used is 0.5 parts by weight to 3 parts by weight.

[0015] According to another embodiment of the present invention, the amount of the core layer used is 100 parts by weight, and the amount of the surface crosslinking agent used is 0.001 parts by weight to 10 parts by weight.

[0016] According to another embodiment of the present invention, the acyclic monoterpene alcohol is selected from at least one of the group consisting of linalool, nerol, geraniol, citronellol and lavenderol.

[0017] According to another embodiment of the present invention, the adjuvant further comprises a monocyclic terpene alcohol having 10 carbon atoms.

[0018] According to another embodiment of the present invention, the amount of the core layer used is 100 parts by weight, and the amount of the auxiliary agent used is 0.01 parts by weight to 1.00 parts by weight.

[0019] According to another embodiment of the present invention, the ratio of the surface crosslinking agent to the auxiliary agent is 4 to 40.

[0020] According to another aspect of the present invention, a water-absorbing resin is provided. This water-absorbing resin is prepared by the aforementioned method for manufacturing water-absorbing resin, wherein the water absorption ratio of the water-absorbing resin under pressure is not less than 21.5 g / g.

[0021] According to another embodiment of the present invention, the water-absorbing resin comprises a core layer and a shell layer, the shell layer covering the outer surface of the core layer, and the surface porosity of the core layer is from 0.020 cc / g to 0.075 cc / g.

[0022] The water-absorbing resin and its manufacturing method of the present invention are described in that a specific amount of foaming agent is first used to polymerize an acid-containing monomer to obtain a core layer with a specific surface porosity, and then an acyclic monoterpene alcohol having 10 to 12 carbon atoms and a surface crosslinking agent are used to perform a surface crosslinking reaction on this core layer, so that the resulting water-absorbing resin has both good water absorption properties and superior deodorizing effect. Attached Figure Description

[0023] To gain a more complete understanding of the embodiments and advantages of the present invention, please refer to the following description and the accompanying drawings. It must be emphasized that the various features are not depicted to scale and are for illustrative purposes only. The relevant drawings are explained below: Figure 1 A flowchart illustrating a method for manufacturing a water-absorbing resin according to an embodiment of the present invention is provided. Detailed Implementation

[0024] The manufacture and use of embodiments of the present invention are discussed in detail below. However, it will be understood that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific embodiments discussed are for illustrative purposes only and are not intended to limit the scope of the invention.

[0025] The method for manufacturing the absorbent resin of the present invention involves controlling the polymerization reaction of acid-containing monomers under pressure and sealing to obtain a core layer (i.e., the preliminary absorbent resin described later) with a surface porosity of 0.020 cc / g to 0.075 cc / g using a foaming agent of greater than 0 parts by weight and not more than 3.14 parts by weight. Then, this core layer is subjected to a surface crosslinking reaction using an acyclic monoterpene alcohol with 10 to 12 carbon atoms and a surface crosslinking agent to form a shell layer on the surface of the core layer. This shell layer contains organic acid ester bonds formed by the esterification reaction of the alcohol groups of the acyclic monoterpene alcohol with the acrylic groups of the core layer. When the absorbent resin comes into contact with urine, the aforementioned surface porosity increases the adsorption of odorous gases from the urine. Furthermore, the urine hydrolyzes the aforementioned organic acid ester bonds, releasing the acyclic monoterpene alcohol, which has a pleasant aroma and removes the odor. Therefore, the resulting absorbent resin possesses both excellent water absorption properties and superior deodorizing effects.

[0026] Please see Figure 1 The method 100 for manufacturing a water-absorbing resin includes providing an acid-containing monomer, an initiator, a foaming agent and an internal crosslinking agent, and performing a polymerization reaction on the acid-containing monomer in a pressure-sealed device to obtain a core layer, as shown in operation 110.

[0027] The acid-containing monomer is a water-soluble unsaturated monomer. In some embodiments, the acid-containing monomer may include, but is not limited to, acrylic acid compounds, other suitable monomeric compounds containing acidic unsaturated double bonds, or combinations thereof. In some specific examples, the acrylic acid compound may include, but is not limited to, acrylic acid, methacrylic acid, 2-propyleneamine-2-methylpropanesulfonic acid, or combinations thereof. In other specific examples, other suitable acid-containing monomeric compounds may include, but are not limited to, maleic acid, maleic anhydride, fumaric acid, and fumaric anhydride, etc., unsaturated compounds containing acidic groups. Only one acid-containing monomer may be used, or multiple acid-containing monomers may be used.

[0028] In other embodiments, the acid-containing monomer may selectively include other hydrophilic monomer compounds having unsaturated double bonds. In some specific examples, these other hydrophilic monomer compounds having unsaturated double bonds may include, but are not limited to, compounds with unsaturated double bonds such as acrylamide, methacrylamide, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, methyl acrylate, ethyl acrylate, dimethylamine acrylamide, and chloroacrylamidotrimethylammonium. There is no particular limitation on the amount of these selectively added acid-containing monomer compounds used, provided that the physical properties of the absorbent resin are not reduced.

[0029] Acid-containing monomers are dissolved in water to form an aqueous solution of acid-containing monomers. The pH of the aqueous solution of acid-containing monomers can be adjusted by neutralizing some of the carboxylic acid groups of the acid-containing monomers to control the pH of the finished superabsorbent resin. In some embodiments, the pH of the aqueous solution of acid-containing monomers is not less than 5.5, and preferably 5.6 to 6.5. When the pH of the aqueous solution of acid-containing monomers is not less than 5.5, the residual monomer content in the gel formed by its polymerization is low, thereby improving the physical properties of the superabsorbent resin.

[0030] Neutralizing agents are used to neutralize the aforementioned acidic monomers. In some embodiments, the neutralizing agent may comprise, but is not limited to, hydroxides of alkali group metals or alkaline earth elements, carbonates, or combinations thereof, and / or other suitable basic compounds. In one specific example, the neutralizing agent may comprise, but is not limited to, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, ammonia compounds, or combinations thereof. Furthermore, only one neutralizing agent may be used, or a mixture of multiple neutralizing agents may be used.

[0031] After neutralization, the acid groups of the acid-containing monomers can form salts such as sodium, potassium, or ammonium salts. In some embodiments, the neutralization concentration can be from 45 mol% to 85 mol%, and more preferably from 50 mol% to 75 mol%. When the degree of neutralization of the aqueous solution of the acid-containing monomers is within the aforementioned range, the pH of the finished absorbent resin product is slightly acidic or neutral, and will not irritate human skin.

[0032] There is no particular limitation on the amount of acid-containing monomer used. Preferably, based on 100 parts by weight of the aqueous solution of the acid-containing monomer, the amount of the acid-containing monomer used is 20 to 55 parts by weight, and more preferably 30 to 45 parts by weight. When the amount of the acid-containing monomer used is 20 to 55 parts by weight, the polymerized gel is not too soft or sticky, which is conducive to mechanical processing, and the concentration of the aqueous solution of the acid-containing monomer is not close to the saturation concentration, which makes it easy to prepare, and the polymerization reaction can be carried out gently, making it easy to control the heat of reaction.

[0033] In some embodiments, the aqueous solution containing acidic monomers may selectively include water-soluble polymers to reduce costs. Specifically, the water-soluble polymers may include, but are not limited to, partially or fully saponified polyvinyl alcohol, polyethylene glycol, polyacrylic acid, polyacrylamide, starch, and / or starch derivatives. Starch and its derivatives may include polymers such as methylcellulose, methylcellulose acrylate, and ethylcellulose. The molecular weight of the aforementioned water-soluble polymers is not particularly limited. Preferably, the water-soluble polymers may be starch, partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and combinations thereof.

[0034] Based on the use of 100 parts by weight of the aqueous solution containing acidic monomers, the use of water-soluble polymers can be 0 to 20 parts by weight, preferably 0 to 10 parts by weight, and even more preferably 0 to 5 parts by weight. When the use of water-soluble polymers is within the aforementioned range, the physical properties of the water-absorbing resin will not be reduced.

[0035] Initiators are used to generate free radicals, thereby initiating the polymerization reaction. Initiators may include, but are not limited to, thermally decomposable initiators, redox initiators, or combinations thereof. In the combination of a redox initiator and a thermally decomposable initiator, the redox initiator first generates free radicals. These free radicals transfer to the acid-containing monomer, thus initiating the first stage of free radical polymerization. The first stage of free radical polymerization releases a large amount of heat, and the resulting high temperature reaches the decomposition temperature of the thermally decomposable initiator. This high temperature triggers the decomposition of the thermally decomposable initiator, thereby initiating the second stage of free radical polymerization, thus enhancing the completeness of the free radical polymerization reaction.

[0036] In some embodiments, the thermally decomposable initiator may comprise a peroxide and / or an azo compound. In some specific examples, the peroxide may comprise, but is not limited to, hydrogen peroxide, di-tert-butyl peroxide, peroxyamide, or persulfate (such as ammonium salts and alkali metal salts). In other specific examples, the azo compound may comprise, but is not limited to, 2,2'-azobis(2-amidinylpropane) dihydrochloride or 2,2'-azobis(N,N-diethylmethylisobutylamidinium) dihydrochloride. In still other embodiments, the redox initiator may comprise, but is not limited to, acidic sulfites, thiosulfates, ascorbic acid, or ferrous salts.

[0037] In some embodiments, based on the weight of the acrylate (i.e., the amount of neutralized acid-containing monomer used) being 100% by weight, the amount of initiator used can be from 0.001% to 10% by weight, and preferably from 0.1% to 5% by weight. When the amount of initiator used is within the aforementioned range, the free radical polymerization rate is moderate, and the heat of reaction is easily controlled, which facilitates the adjustment of the degree of polymerization.

[0038] An internal crosslinking agent is used to crosslink the acid-containing monomers to give the resulting core layer mechanical processability. The internal crosslinking agent may be added to an aqueous solution of the unreacted acid-containing monomers before polymerization. The internal crosslinking agent may comprise, but is not limited to, compounds having at least two unsaturated double bonds, compounds having at least two epoxy groups, or combinations of the foregoing.

[0039] In some specific examples, compounds having at least two unsaturated double bonds may include, but are not limited to, N,N'-bis(2-propenyl)amine, N,N'-methylenebisacrylamide, N,N'-methylenebismethylacrylamide, propylene acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, glycerol triacrylate, glycerol trimethacrylate, glycerol triacrylate with ethylene oxide or trimethacrylate, triethanolamine propane triacrylate with ethylene oxide or trimethacrylate, triethanolamine propane trimethacrylate, triethanolamine propane triacrylate, N,N,N-tri(2-propenyl)amine, ethylene glycol diacrylate, polyoxyethylene glycerol triacrylate, diethyl polyoxyethylene glycerol triacrylate, dipropylene triethylene glycol ester, or combinations thereof.

[0040] In some specific examples, compounds having at least two epoxy groups may include, but are not limited to, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, diglycerol polyglycidyl ether, or combinations thereof. Furthermore, only one internal crosslinking agent or multiple internal crosslinking agents may be used.

[0041] In some embodiments, based on a total usage of 100 parts by weight of the neutralized acidic monomer, internal crosslinking agent, initiator, and foaming agent, the usage of the internal crosslinking agent is from 0.001 parts by weight to 5 parts by weight, and preferably from 0.01 parts by weight to 3 parts by weight. When the usage of the internal crosslinking agent is within the aforementioned range, the polymerized gel is non-sticky, which facilitates mechanical processing, and the polymerized gel has good water absorption, thereby improving the performance of the water-absorbing resin.

[0042] Foaming agents are used to generate non-toxic gases (such as carbon dioxide) during the polymerization reaction to give the core layer surface pores. These pores increase the adsorption capacity for odorous gases produced by urine and bacteria in urine. Therefore, the polymerization reaction must be carried out in a pressure-sealed device to retain the non-toxic gases. For example, a pressure-sealed device can be a conventional batch reaction vessel, such as a batch reactor.

[0043] In some embodiments, the foaming agent may comprise alkali metal carbonates and / or alkaline earth metal carbonates. These carbonates can undergo acid-base neutralization with acid-containing monomers and / or acid-containing initiators to produce carbon dioxide. Specifically, based on 100 parts by weight of the acid-containing monomer, the amount of foaming agent used can be greater than 0 parts by weight and not more than 3.14 parts by weight, and preferably 0.5 parts by weight to 3 parts by weight. When the amount of foaming agent used is within the aforementioned range, a suitable amount of gas can be generated to give the core layer an appropriate surface porosity (e.g., 0.020 cc / g to 0.075 cc / g), and this appropriate surface porosity can uniformly absorb subsequent surface crosslinking agents to facilitate subsequent crosslinking reactions, thereby maintaining the water absorption ratio of the water-absorbing resin under pressure at not less than 21.5 g / g. In other words, an appropriate amount of foaming agent can improve the deodorizing effect of the water-absorbing resin without reducing its water absorption characteristics.

[0044] In some embodiments, the gel obtained by the polymerization reaction (i.e., the initial absorbent resin and the aforementioned core layer) can first be cut into gel particles with a particle size of no more than 20 mm using a shredder, and preferably no more than 10 mm. Then, the screening described later is performed.

[0045] Next, gel particles with a fixed particle size of no more than 2.00 mm are screened out, preferably between 0.05 mm and 1.50 mm. If the gel particles have a particle size greater than 2.00 mm, they are returned to the reactor for further shredding. If the gel particles have a particle size less than 0.05 mm, the amount of fine powder in the finished absorbent resin product is easily increased after drying and shredding. If the gel particles have a particle size greater than 2.00 mm, poor heat conduction during drying can easily lead to a high residual monomer content and undesirable physical properties in the finished absorbent resin product. According to the present invention, the narrower the particle size distribution of the gel particles, the better the physical properties of the gel particles after drying, and it is also beneficial to control the drying time and temperature.

[0046] In some embodiments, the gel particles are screened and then dried, wherein the drying temperature can be between 100°C and 180°C. When the drying temperature is below 100°C, the required drying time is long, which is not economical. When the drying temperature is above 180°C, the internal cross-linking agent will undergo cross-linking reaction prematurely. In the subsequent drying process, the excessive degree of cross-linking makes it impossible to effectively remove residual monomers, thus failing to reduce the amount of residual monomers.

[0047] In some embodiments, after drying, the gel particles are pulverized and screened to fix their particle size. The screened fixed particle size is 0.06 mm to 1.00 mm, and preferably 0.10 mm to 0.85 mm. When the fixed particle size is less than 0.06 mm, the fine powdery gel particles increase the dust content of the absorbent resin product. When the particle size of the gel particles is greater than 1.00 mm, the gel particles reduce the water absorption rate of the absorbent resin product. According to the present invention, the narrower the particle size distribution of the gel particles, the better.

[0048] To improve the water-absorbing properties of colloids, such as strength, absorption rate, anti-caking properties, and liquid permeability, surface crosslinking treatment can be applied to water-absorbing resin particles. Numerous patent documents have disclosed surface crosslinking treatments. For example, in Japanese Patent Publications Nos. 1981-131608, 1982-44627, 1983-42602, and 1983-117222, surface crosslinking treatment is performed by dispersing a preliminary water-absorbing resin and a crosslinking agent in an organic solvent. In Japanese Patent Publications Nos. 1985-163956 and 1985-255814, surface crosslinking treatment is performed by directly mixing an inorganic powder with a crosslinking agent and a crosslinking agent solution into the water-absorbing resin. In Japanese Patent Publication No. 1989-113406, surface crosslinking treatment is performed by steam treatment after adding a crosslinking agent. In Japanese Patent Publication No. 1989-292004 and US Patent Publication No. 6346569, surface treatment was performed using organic solvents, water, and polyols. In Japanese Patent Publication No. 1990-153903, surface treatment was performed using organic solutions, water, and ether compounds. While these surface crosslinking treatments can increase the absorption rate and water absorption ratio under pressure of the absorbent resin, they significantly reduce its holding power, thereby reducing its performance in practical applications. However, the surface crosslinking treatment of the present invention does not suffer from the above-mentioned disadvantages.

[0049] Please refer to the following: Figure 1 Following operation 110, a surface crosslinking agent and an auxiliary agent are provided, and the core layer undergoes a surface crosslinking reaction to form a shell layer, as shown in operation 120. In some embodiments, the surface crosslinking agent may comprise a polyol, a polyamine, a compound having at least two epoxy groups, a hydrocarbon ester, or a combination thereof.

[0050] Specific examples of the aforementioned polyols may include, but are not limited to, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and propylene glycol. Specific examples of the aforementioned polyamines may include, but are not limited to, ethylenediamine, diethylenediamine, and triethylenediamine. Specific examples of the aforementioned compounds having at least two epoxy groups may include, but are not limited to, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and diglycerol polyglycidyl ether.

[0051] Specific examples of the aforementioned hydrocarbon carbonates may include, but are not limited to, ethylene glycol carbonates, 4-methyl-1,3-dioxacyclopentan-2-one, 4,5-dimethyl-1,3-dioxacyclopentan-2-one, 4,4-dimethyl-1,3-dioxacyclopentan-2-one, 4-ethyl-1,3-dioxacyclopentan-2-one, 1,3-dioxacyclohexan-2-one, 4,6-dimethyl-1,3-dioxacyclohexan-2-one, and 1,3-dioxacycloheptan-2-one. Furthermore, only one surface crosslinking agent may be used, or multiple surface crosslinking agents may be used.

[0052] Based on the core layer being used in an amount of 100 parts by weight, the surface crosslinking agent being used in an amount of 0.001 parts by weight to 10 parts by weight, preferably 0.005 parts by weight to 5 parts by weight, and even more preferably 0.5 parts by weight to 3 parts by weight. When the amount of surface crosslinking agent used is within the aforementioned range, the crosslinking effect on the surface of the water-absorbing resin is significant, thus improving its water absorption.

[0053] Depending on the type of surface crosslinking agent, the surface crosslinking agent can be added directly or by preparing a solution. The solvent used in the solution can be water or a hydrophilic organic solvent, such as methanol, ethanol, propanol, isobutanol, acetone, dimethyl ether, and diethyl ether. In some embodiments, the hydrophilic organic solvent is preferably methanol or ethanol, as disclosed in U.S. Patent Publication No. 6,849,665.

[0054] In the method 100 for manufacturing the absorbent resin of the present invention, an auxiliary agent and a surface crosslinking agent can be mixed, and then the mixed solution of the two can be coated onto the surface of the core layer to carry out a surface crosslinking reaction. For example, at least one of the surface crosslinking agent and the auxiliary agent can be prepared into a solution first, and then the other can be added to the prepared solution. In another specific example, the surface crosslinking agent and the auxiliary agent are mixed to form a mixture, wherein the mixture can be used directly to carry out the surface crosslinking reaction, or the mixture can be prepared into a solution with a solvent before carrying out the surface crosslinking reaction. The alcohol group of the auxiliary agent can undergo an esterification reaction with the acrylic group on the surface of the core layer to form an ester bond. When urine comes into contact with the absorbent resin, the urine can hydrolyze the ester bond to release the fragrance-containing auxiliary agent, thereby exerting a deodorizing effect.

[0055] The adjuvant contains acyclic monoterpenoids, wherein the acyclic monoterpenoids have 10 to 12 carbon atoms. If the adjuvant does not contain acyclic monoterpenoids with 10 to 12 carbon atoms, the absorbent resin cannot release the pleasantly scented acyclic monoterpenoids upon contact with urine, thus failing to deodorize effectively. In some embodiments, the acyclic monoterpenoids are selected from at least one of the group consisting of linalool, nerol, geraniol, citronellol, and lavenderol. For example, these acyclic monoterpenoids may be contained in extracts such as rose, rue, citronella, lemon, and lavender.

[0056] In a preferred embodiment, the adjuvant may selectively include monocyclic terpenoids, wherein the monocyclic terpenoids have 10 to 12 carbon atoms. When the adjuvant includes monocyclic terpenoids with 10 to 12 carbon atoms, the absorbent resin may further release the monocyclic terpenoids upon contact with urine, thereby providing the user with a layered fragrance experience through the monocyclic terpenoids. In detail, although the acyclic monoterpenoids of the present invention have a more pleasant fragrance than the monocyclic terpenoids of the present invention, they can provide better deodorizing effects. However, if only acyclic monoterpenoids are used for deodorization, the olfactory organs become desensitized to the same fragrance after a period of time (e.g., 1 to 3 minutes). Therefore, using a combination of acyclic monoterpenoids and monocyclic terpenoids can provide a layered fragrance experience, thereby improving the deodorizing effect and increasing olfactory comfort.

[0057] In some specific examples, monocyclic terpenoids are selected from at least one of the group consisting of menthol, terpineol, carvacrol, and perillol. Similar to acyclic monoterpenoids, these monocyclic terpenoids can also be extracted from plants such as laurel, rosemary, anise, sage, and turmeric. Furthermore, compared to glycosides formed through glycoside formation reactions of monoterpenoids (such as extracts from soapberry), acyclic and monocyclic terpenoids have higher volatility and more pleasant aromas, thus providing deodorizing effects. Since these adjuvants are obtained from natural plants, the resulting absorbent materials are non-toxic and non-irritating to human skin, providing long-term comfort.

[0058] In some embodiments, based on the core layer being used in an amount of 100 parts by weight, the amount of auxiliary agent being used is from 0.01 parts by weight to 1.00 parts by weight, preferably from 0.05 parts by weight to 1.00 parts by weight. When the amount of auxiliary agent used is within the aforementioned range, an appropriate amount of auxiliary agent can improve the deodorizing effect without reducing the crosslinking effect of the surface crosslinking agent.

[0059] The ratio of surface crosslinking agent to auxiliary agent is 4 to 40, and preferably 1. When this ratio is within the aforementioned range, the surface crosslinking agent and auxiliary agent can simultaneously provide better crosslinking and deodorizing effects, thus enabling the water-absorbing resin to have both better water absorption properties and deodorizing effect.

[0060] On the other hand, the absorbent resin used as the absorbent core of a diaper not only needs to possess a certain level of retention (such as the ability to absorb liquid), but also needs to have a high absorbency ratio under pressure (such as not less than 21.5 g / g). The absorbency ratio under pressure indicates whether the absorbent resin will break down due to external pressure (such as the baby's weight) after absorbing liquid. Damaged absorbent resin not only loses its ability to absorb liquid, but also leaks the liquid already absorbed into the resin, thus increasing the rewet rate and significantly reducing the diaper's dryness. Generally, when the absorbency index under pressure (AAP) of the absorbent resin is not less than 0.8, the rewet rate of the absorbent resin core can be significantly reduced.

[0061] In some specific examples, the absorbent resin obtained by the present invention can be applied to hygiene products such as diapers (e.g., low-concentration pulp diapers (Fluffless, which uses a large amount of absorbent resin at the same time) or adult diapers), so that the diapers have both good absorbency and deodorization capabilities.

[0062] In some applications, the absorbent of the present invention is formed by molding a water-absorbing resin and hydrophilic fibers to form a sheet-like absorbent, the absorbent having a surface layer composed of an impermeable polyethylene (PE) film and a liquid-permeable nonwoven fabric underneath; or the water-absorbing resin is fixed to a pulp fiber material (Airlaid) and / or a nonwoven fabric, wherein the pulp fiber may be pulverized wood pulp, cross-linked cellulose fiber, cotton, wool or vinyl acetate fiber.

[0063] Based on a 100% weight percentage of absorbent, the content of absorbent resin (core concentration) is 20% to 100% by weight, preferably 40% to 100% by weight, and even more preferably 50% to 100% by weight. Using such a high content of absorbent resin in the core concentration significantly enhances the antibacterial and deodorizing effects of the present invention.

[0064] Generally, the basis weight (weight per unit area) of the absorbent of the present invention can be 0.01 g / cm³. 2 Up to 0.30 g / cm 2 Furthermore, the thickness of the absorber is no more than 30 mm.

[0065] The following examples illustrate the application of the present invention, but are not intended to limit the invention. Any person skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention.

[0066] Preparation of preliminary water-absorbing resin particles (i.e., core layer) Preparation Example 1 The preliminary preparation of the absorbent resin particles in Example 1 was carried out in a conical flask. 583.2 g of water and 540 g of acrylic acid were placed in the flask and stirred evenly. Then, 437.5 g of 48% sodium hydroxide aqueous solution was added dropwise into the conical flask and the temperature was maintained at 15°C to 40°C for 2 hours. The dropwise addition ratio of sodium hydroxide to acrylic acid was 0.85 to 0.95 to obtain a sodium acrylate aqueous solution with a monomer concentration of 42 parts by weight, wherein 70 mol% of acrylic acid was partially neutralized to form sodium acrylate.

[0067] The sodium acrylate aqueous solution was transferred to a batch reactor (manufactured by Chi Yen Precision Machinery Co., Ltd.), and N,N'-methylenebisacrylamide was added. The temperature was maintained at approximately 20°C, and then hydrogen peroxide, sodium bisulfite, ammonium persulfate, and sodium carbonate aqueous solution were added to carry out a free radical polymerization reaction. Next, the resulting gel was shredded using a shredder, and gel particles with a diameter no greater than 2 mm were sieved out.

[0068] The gel particles were dried at 130°C for 2 hours and then sieved through a sieve with a fixed particle size of 0.1 mm to 0.85 mm to obtain preliminary water-absorbing resin particles. Then, tests were conducted using the evaluation methods described later.

[0069] Preparation Example 2 and Comparative Preparation Examples 1 to 3 Preparation Example 2 and Comparative Examples 1 to 2 were prepared using a method similar to that of Preparation Example 1. The difference was that the amount of sodium carbonate used in Preparation Example 2 and Comparative Examples 1 to 2 was changed. Comparative Example 3 involved dissolving 425.2 g of acrylic acid, 4499.5 g of a 37% by weight aqueous solution of sodium acrylate, 538.5 g of pure water, 6.17 g of polyethylene glycol diacrylate (molecular weight 523 g / mole), and 0.21 g of trisodium diethylenetriaminepentaacetate to obtain a mixed solution. Then, 28.3 g of a 10% by weight aqueous solution of sodium bisulfite and 23.6 g of a 0.1% by weight aqueous solution of L-ascorbic acid were added to the mixed solution to carry out a polymerization reaction, thereby obtaining preliminary water-absorbing resin particles. Detailed formulations and evaluation results for Preparation Examples 1 to 2 and Comparative Examples 1 to 3 are shown in Table 1.

[0070] Preparation of the shell Example 1 The shell layer of Example 1 was prepared by mixing ethylene glycol, 1,4-butanediol, and methanol in a volume ratio of 1:1:0.5. 5g of this mixture, along with an auxiliary agent, was added to 200g of preliminary absorbent resin particles, and the mixture was heated to 150°C for 1 hour, followed by cooling to obtain the absorbent resin of Example 1. The following evaluation method was then used for testing.

[0071] Examples 2 to 6 and Comparative Examples 1 to 7 Examples 2 to 6 and Comparative Examples 1 to 7 were prepared using a method similar to that of Example 1. The difference lies in the use of different initial water-absorbing resin particles, surface crosslinking agents, and auxiliary agents in Examples 2 to 6 and Comparative Examples 1 to 7. In Comparative Example 7, the auxiliary agents were tea extract solution and bamboo extract solution. Detailed formulations and evaluation results for Examples 1 to 6 and Comparative Examples 1 to 7 are shown in Table 2.

[0072] Manufacturing of absorbers Application Example 1 The absorbent in Application Example 1 was manufactured by mixing 10.0 g of the absorbent resin from Example 1 with 10.0 g of pulverized wood pulp using an absorbent forming machine. The forming mesh was a 400-mesh (38 μm) metal mesh, and the absorbent area was 160 square centimeters (8 cm × 20 cm). The formed absorbent was then placed on a PE film, followed by a non-woven fabric. A pressure of 18.39 kPa (e.g., 30 kg of weight applied to a 160 square centimeter area) was then applied. After applying pressure for 5 minutes, the edges were glued together with white adhesive to obtain the absorbent of Application Example 1.

[0073] Application Examples 2 to 6 and Comparative Application Examples 1 to 7 Application Examples 2 to 6 and Comparative Application Examples 1 to 7 were all formulated using the same method as Application Example 1. The difference was that Application Examples 2 to 6 and Comparative Application Examples 1 to 7 used the water-absorbing resins prepared in Examples 2 to 6 and Comparative Application Examples 1 to 7, respectively. Furthermore, the evaluation results of the absorbents in Application Examples 1 to 6 and Comparative Application Examples 1 to 7 are shown in Table 3.

[0074] Evaluation method Unless otherwise stated, all evaluation methods described below are conducted at room temperature (23±2℃) and relative humidity of 45±10%.

[0075] 1. Holding force test The centrifuge retention capacity (CRC) test was conducted in accordance with the test method specified by EDANA in ERT241.2(12).

[0076] 2. Surface porosity test Surface porosity was tested at a standard filling pressure of 4 kPa and measured using a mercury micromeritics instrument (AutoPore, model IV 9520).

[0077] 3. Test of water absorption ratio under pressure The pressure uptake ratio (AAP) test was conducted according to the test method of ERT 442.3(10) specified by the European Nonwovens Association (EDANA), in which the uptake ratio of the absorbent resin to a 0.9% sodium chloride aqueous solution was measured at a pressure of 4.9 kPa and a test time of 60 minutes.

[0078] 4.0.9% saline solution absorption rate test The test for the absorption rate of 0.9% saline solution was conducted in accordance with the test method of ERT 240.2(12) specified by EDANA.

[0079] 5. Test on water absorption rate in one minute The test of the one-minute water absorption ratio was conducted in accordance with the test method of EDANA ERT 240.2(12), but deionized water was used instead of saline solution and the absorption time was changed (from 30 minutes to 1 minute).

[0080] 6. Core Shell Absorption Against Pressure (CS AAP) Test The test for water absorption ratio under shell pressure was conducted in accordance with the aforementioned test method for water absorption ratio under pressure, but the test time was extended to 240 minutes.

[0081] 7. Absorption Index under Pressure (Index of AAP) The pressure absorption index is calculated using the aforementioned pressure absorption ratio and shell-core pressure absorption ratio, and obtained through the following formula (I): Absorption index under pressure = (I).

[0082] 8. Odor removal rating test The deodorization level test involved adding 2.5g of adult urine (tested within two hours of excretion) and 2.0g of absorbent resin to a polypropylene bottle, capping the bottle, and placing it at 37°C for 2 hours. Next, the odor was smelled manually from approximately 3cm above the bottle opening, and the odor level was evaluated according to the specific criteria below. The average odor level evaluated by 10 adults was used as the deodorization level to assess the deodorization effect. The specific evaluation criteria are shown below, with level 5 based on the odor of urine without added absorbent resin: 0: Odorless; 1: A slight odor can be detected; 2: An odor can be smelled, but the odor is within a tolerable range; 3: A foul odor is detected, and the odor is close to the limit of tolerance; 4: A very strong odor is detected, and the odor is slightly greater than the tolerable limit; 5: A strong odor is detected, and the odor is far beyond the tolerance limit.

[0083] 9. Test on odor removal rate The odor removal rate was tested by adding 1.0 g of the test absorbent resin and 25 mL of 0.03% sodium methanethiol aqueous solution to a 1-liter sealed container and incubating at room temperature for 10 minutes. The concentration of residual gas was analyzed using gas detection tubes (manufactured by GASTEC, models 4L and 4HM) to obtain the results for the test group. In a separate test without the use of absorbent resin, the concentration of residual gas was analyzed using the same gas detection tubes to obtain the results for the blank group. The removal rate of methanethiol was calculated according to formula (II).

[0084] Removal rate (%) = ×100% (II) 10. Test for synthetic urine re-osmosis The test for synthetic urine re-osmosis volume was performed by applying 4.8 kPa (over an area of ​​160 cm²). 2 A 7.8 kg weight was applied evenly to the absorber. Then, synthetic urine (Jayco synthetic urine as described in US Patent Publication No. 20040106745) was added in three portions, totaling 180 ml, at a frequency of once every 30 minutes, to the center of the absorber. After adding the synthetic urine, the weight was removed after another 30 minutes. Thirty sheets of filter paper (each with an area of ​​8 cm × 20 cm) weighed to a total weight (W1(g)) were placed on the absorber, and the weight was immediately placed on the absorber for 5 minutes to allow the filter paper to absorb the reabsorbed synthetic urine. The weight of the 30 sheets of filter paper (W2(g)) was then measured, and the weight difference (W2 minus W1) was used as the amount of synthetic urine reabsorbed into the absorber. A lower reabsorbed amount indicates better drying properties of the absorbent resin.

[0085] 11. Deodorization test of the absorbent The deodorization test of the absorbent was conducted using the same method as the aforementioned deodorization grade test of the absorbent resin. The difference was that the absorbent deodorization test involved placing a 10×10 square centimeter absorbent in a glass petri dish (with an inner diameter of 120 mm) and then adding 2.5 g of adult urine to the absorbent.

[0086] Table 1

[0087] “N / A” indicates that this test was not performed. “-” indicates that this component was not used.

[0088] Table 2

[0089] "-" indicates that this component is not used.

[0090] Table 3

[0091] Please refer to Table 1. Examples 1 to 6 all use a preliminary water-absorbing resin prepared with a foaming agent (i.e., using the method of preparation example 1 or 2) and an acyclic monoterpene alcohol with 10 to 12 carbon atoms. Therefore, the water-absorbing resin prepared can have both good water absorption properties and excellent deodorization effect.

[0092] However, compared to Examples 1 to 6, Comparative Examples 1 to 5 all used a preliminary absorbent resin that was not prepared with a foaming agent (i.e., using the method of Preparation Example 3), and Comparative Example 1 did not use an auxiliary agent, while Comparative Examples 2 to 5 used an auxiliary agent. Therefore, the absorbent resins obtained only had good water absorption properties and deodorizing effects. Secondly, compared to Comparative Examples 2 to 3 which used monocyclic terpene alcohols, Comparative Examples 4 to 5 used acyclic monoterpene alcohols, so the absorbent resins obtained had slightly better deodorizing effects.

[0093] Furthermore, Comparative Example 6 used an excessive amount of foaming agent to prepare the preliminary water-absorbing resin (i.e., using the method of Preparation Example 3), thus the prepared water-absorbing resin had a poor water absorption ratio under pressure, that is, poor water absorption characteristics. In addition, Comparative Example 7 did not use foaming agent or auxiliary agents, but used tea extract and bamboo extract, and the prepared water-absorbing resin had poor deodorizing effect.

[0094] In summary, the water-absorbing resin and its manufacturing method of the present invention first use a foaming agent to polymerize acid-containing monomers to obtain a core layer with a specific surface porosity, and then use a specific acyclic monoterpene alcohol and a surface crosslinking agent to perform a surface crosslinking reaction on this core layer, so that the resulting water-absorbing resin has both good water absorption properties and superior deodorizing effect.

[0095] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Those skilled in the art to which this invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0096] [Symbol Explanation] 100: Method 110, 120: Operation.

Claims

1. A method for manufacturing a water-absorbing resin, characterized in that, Include: A core layer is obtained by polymerizing an acid-containing monomer, an initiator, a blowing agent, and an internal crosslinking agent in a pressure-sealed apparatus. The acid-containing monomer is used in an amount of 100 parts by weight, the blowing agent is used in an amount greater than 0 parts by weight and not greater than 3.14 parts by weight, the acid-containing monomer is a mixture of acrylic acid and sodium acrylate, the blowing agent contains an alkali metal carbonate and / or an alkaline earth metal carbonate, and the surface porosity of the core layer is from 0.020 cc / g to 0.069 cc / g. A surface crosslinking agent and an auxiliary agent are provided, and a surface crosslinking reaction is performed on the core layer to form a shell layer, wherein the shell layer covers the outer surface of the core layer, and the auxiliary agent comprises an acyclic monoterpene alcohol having 10 to 12 carbon atoms.

2. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, Based on the amount of the acid-containing monomer used being 100 parts by weight, the amount of the foaming agent used is 0.5 to 3 parts by weight.

3. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, Based on the use of 100 parts by weight of the core layer, the use of the surface crosslinking agent is from 0.001 parts by weight to 10 parts by weight.

4. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, The acyclic monoterpene alcohol is selected from at least one of the group consisting of linalool, nerol, geraniol, citronellol and lavenderol.

5. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, The adjuvant also contains a monocyclic terpene alcohol with 10 carbon atoms.

6. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, Based on the use of 100 parts by weight of the core layer, the use of the auxiliary agent is from 0.01 parts by weight to 1.00 parts by weight.

7. The method for manufacturing the water-absorbing resin according to claim 1, characterized in that, The ratio of the surface crosslinking agent to the auxiliary agent used is 4 to 40.

8. A water-absorbing resin, characterized in that, The water-absorbing resin is prepared by a method for manufacturing a water-absorbing resin according to any one of claims 1 to 7, wherein the water absorption ratio of the water-absorbing resin under pressure is not less than 21.5 g / g.

9. The water-absorbing resin according to claim 8, characterized in that, The absorbent resin comprises a core layer and a shell layer, with the shell layer covering the outer surface of the core layer.

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